Hydrogen production by catalytic decomposition of selected hydrocarbons and H2O dissociation over CeZrO2 and Ni/CeZrO2

Presented paper deals with the catalytic decomposition of hydrocarbons (methane and toluene) in the aspect of H₂ production and types of obtained carbon deposits. The catalyst used in our studies was nickel supported on ceria–zirconia (Ni/CeZrO₂). The aim of this work was to investigate the reactivity of obtained carbon deposits with H₂O. Both issues are of great importance for determining the mechanisms of carbon deposits formation and their suppression during steam reforming reaction.     

Ni doped carbons for hydrogen production by catalytic methane decomposition

Ni doped carbons were prepared from raw coal and direct coal liquefaction residue (CLR) by KOH activation with addition of Ni(NO₃)₂, and used for catalytic methane decomposition (CMD) to produce hydrogen. The catalytic activity of the Ni doped carbon for CMD was compared with those of metal catalysts (Ni/SiO₂ and Ni/Al₂O₃), coal- and CLR-based carbons, and Ni-carbon catalysts prepared by traditional impregnation and precipitation methods. The results show that the Ni doped carbon has higher and more stable activity than the metal and carbon catalysts at 850 °C. The preparation method for Ni doped carbons can make full use of the reducibility of the carbon composition and simplify the traditional synthesis process. The Ni content and the morphology of carbon deposits produced during CMD have a great effect on the catalytic activity of the Ni doped carbon.     

Reliability of multilayer ceramic capacitors with nickel electrodes

The reliability of multilayer ceramic capacitors (MLCCs) with Ni internal electrodes has been studied trom the viewpoint of partial oxygen pressure (P_O2) during firing. It is shown that the load-life time of the insulation resistance (1R) was prolonged by firing under low Po₂ annealing after firing, and the addition of dopants. It is also shown that the generation of oxygen vacancies led to the degradation of IR. Annealing treatment for the oxidation of the dielectric body accelerates the dielectric aging of MLCCs. It is found that the appropriate control of the P_O2 during firing can improve the reliability of MLCCs with Ni electrodes to a level as high as that of MLCCs with precious metal electrodes. Thus, we have developed an MLCC with Ni electrodes that features high reliability and a large capacitance of 10 μF for the Y5V characteristic and 4.7 μF for the X7R characteristic, both in the case of the C3216 (3.2 mm × 1.6 mm × 1.4 mm) form.     

MOF衍生的高选择性加氢芳香硝基化合物的石墨碳包覆镍催化剂

针对芳香硝基化合物的催化选择性加氢反应,开发可替代贵金属催化剂的低成本、高效非贵金属催化剂,对于芳香胺类化合物的绿色生产具有重要意义。利用简易、可规模化的制备方法,以镍—2,5-吡啶二羧酸金属有机框架为前驱体,热解制备了氮掺杂石墨碳包覆镍纳米催化材料（Ni@CN）。采用X射线衍射、扫描电镜、透射电镜、元素分析、N2吸脱附等检测手段对Ni@CN的物化性质进行了表征,并对其催化性能进行了评价。结果表明,Ni@CN可在温和条件下（85℃,1.0 MPa H2)高效加氢含取代官能团的芳香硝基化合物生成对应的芳香胺类化合物。对比试验表明,镍纳米颗粒是Ni@CN的加氢活性中心,而石墨碳壳的存在有利于优先吸附硝基官能团。此外,进一步考察了Ni@CN的循环使用性能以及抗硫化物中毒的特性。     

Oxidative Instability of Fuels: Nickel Catalyzed Reactions

The reactions that lead to long-term storage instability of fuels are not fully understood. Various reports in the literature link particular fuels with specific reactions, usually oxidation or free radical processes. Trace quantities of metals are present in all processed fuels. The metal source can be naturally occurring or present from fuel handling. The usual case is to look at the reaction of the metal or metal ion with molecular oxygen or other active oxygen species such as hydroperoxides. This article reports on the reaction of a nitrogen heterocycle, indole. We propose a mechanism that shows that catalytic amounts of nickel can produce compounds of higher molecular weight and increased polarity.     

Combustion synthesis and characterization of NiO nanoparticles

Nickel oxide nanoparticles (NiO NPs) have been prepared by gel-combustion technique using 1:0.5 (N 105) and 1:1 (N 11) weight ratios of oxidizer, nickel nitrate hexahydrate and fuel, cassava starch, respectively. The X-ray diffraction pattern of the samples revealed cubic phase of nickel oxide and the average crystallite size of 28 and 38 nm for N 105 and N 11, respectively, were noted. In comparison to particle size measured using TEM (35 and 60 nm), the average particle size obtained from DLS (250 and 350 nm) was larger for N 105 and N 11, respectively. NiO NPs were found to have indirect band gap (2.98 and 2.3 eV) as revealed by optical spectroscopy. They were tested for energy storage, antimicrobial activity and photocatalytic applications. Electrochemical studies showed NiO NPs had a reversible capacity of 940 and 785 mA h/g for N 105 and N 11, respectively and they retained a capacity of 59% and 47% upto 50 cycles. The antimicrobial activity was tested against two bacterial strains and a fungal strain. The photocatalytic activity was measured for degradation of methylene blue in ultra-violet as well as sunlight. NiO, obtained by using 1:1 oxidizer to fuel ratio, (N 11) exhibited 94% degradation efficiency in sunlight because of a visible light-active band gap (2.3 eV).     

Electrocatalytic oxidation of methanol on Ni and NiCu alloy modified glassy carbon electrode

Nickel and nickel–copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV) and chronoamperometry (CA) were employed. The cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution. In CV studies, in the presence of methanol NiCu alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel hydroxide increase is followed by a decrease in the corresponding cathodic current in presence of methanol. The anodic peak currents show linear dependency with the square root of scan rate. This behavior is the characteristic of a diffusion controlled process. Under the CA regime the reaction followed a Cottrellian behavior and the diffusion coefficient of methanol was found to be 2 × 10⁻⁶ cm² s⁻¹ in agreement with the values obtained from CV measurements.     

Nickel catalysts supported on ZrO2, Y2O3-stabilized ZrO2 and CaO-stabilized ZrO2 for the steam reforming of ethanol: Effect of the support and nickel load

Catalysts with various nickel loads were prepared on supports of ZrO₂, ZrO₂–Y₂O₃ and ZrO₂–CaO, characterized by XRD and TPR and tested for activity in ethanol steam reforming. XRD of the supports identified the monoclinic crystalline phase in the ZrO₂ and cubic phases in the ZrO₂–Y₂O₃ and ZrO₂–CaO supports. In the catalysts, the nickel impregnated on the supports was identified as the NiO phase. In the TPR analysis, peaks were observed showing the NiO phase having different interactions with the supports. In the catalytic tests, practically all the catalysts achieved 100% ethanol conversion, H₂ yield was near 70% and the gaseous concentrations of the other co-products varied in accordance with the equilibrium among them, affected principally by the supports. It was observed that when the ZrO₂ was modified with Y₂O₃ and CaO, there were big changes in the CO and CO₂ concentrations, which were attributed to the rise in the number of oxygen vacancies, permitting high-oxygen mobility and affecting the gaseous equilibrium. The liquid products analysis showed a low selectivity to liquid co-products during the reforming reactions.     

SOFC anodes for direct oxidation of hydrogen and methane fuels containing H2S

Single cell solid oxide fuel cells using Ni-YSZ and Co-YSZ anodes were tested in H₂, CH₄, H₂S/H₂ and H₂S/CH₄ fuel mixtures. Their performance was found to quickly degrade in dry CH₄ due to carbon deposition and lifting of the anode from the electrolyte. In contrast, hydrogen or methane containing H₂S showed an increase in exchange current densities when compared to H₂,M/YSZ/LSM,air systems (M = Ni or Co) despite having less optimal anode microstructure. Conversion from metal to metal-sulfide in the presence of H₂S produced large, dense metal-sulfide particles surrounded by YSZ, thus decreasing the triple-phase boundary. Furthermore, CoS-based anodes showed phase segregation and densification toward the electrolyte. Despite this, long-term testing at η_a = 0.5 V of the H₂S/CH₄,CoS-YSZ/YSZ/LSM,air system showed no signs of degradation of the anode over a 6-day period. Only after removal of H₂S from the H₂S/CH₄ stream did the CoS-anode reduce back to Co, signifying H₂S is required to maintain the metal-sulfide active anode.     

Production of hydrogen by ethanol steam reforming over catalysts from reverse microemulsion-derived nanocompounds

In the present work, hydrotalcite-like compound precursor for preparing mixed oxide catalyst was successfully synthesized by a novel method, which was a combination of the reverse microemulsion and coprecipitation methods. It was observed that the precursor obtained from the above method possessed superior characteristics for preparing mixed oxide catalyst used in ethanol steam reforming (ESR). Furthermore, for comparison, catalysts prepared from conventional coprecipitation and impregnation methods had been characterized together with the catalyst prepared from the new method. Besides ICP, BET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), H₂-TPD, TG, and TEM analytic techniques, catalytic performance for ESR was also investigated. The results of XRD and TPR indicated that a solid solution phase existed in the catalysts obtained from reverse microemulsion and coprecipitation methods, while spinel phase together with solid solution were observed in the catalyst obtained from the impregnation method. The high BET surface area of the catalyst obtained from the reverse microemulsion method enhanced the dispersion and the surface area of nickel, which improved the catalyst performance. From TEM images, the aggregated Ni could be found in the catalyst obtained from the impregnation method, while the hydrotalcite-like compound precursors prepared from reverse microemulsion and coprecipitation methods produced homogeneously distributed active Ni metal species. The catalyst obtained from reverse microemulsion exhibited the best activity, stability, and least carbon deposition because of the formation of hydrotalcite-like compound precursor, uniform dispersion of active Ni metal species, and much more surface area supporting the active Ni metal sites.